Find the First Six Terms (Rounded to Three Decimal Places)

Essay

Find the first six terms (rounded to three decimal places) of the Fourier series. Assume half-wave symmetry.
$\begin{array}{|c|c|c|c|c|c|c|c|c|c|c|}\hline\boldsymbol{x} & 0^{\circ} & 20^{\circ} & 40^{\circ} & 60^{\circ} & 80^{\circ} & 100^{\circ} & 120^{\circ} & 140^{\circ} & 160^{\circ} & 180^{\circ} \\\hline\boldsymbol{y} & 0 & 2.1 & 4.8 & 7.5 & 11.2 & 10.9 & 6.8 & 5.2 & 2.4 & 0 \\\hline\end{array}$